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Thread: Chassis/Armour to weight ratio

  1. #1
    Roboteer

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    Kenneth Gibson
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    Hi guys
    Currently working on designing a new hw bot.

    Just a question any ideas on what the average weight of cassis and armour mass is on a heavyweight combat robot?

    I am aware of that depends on design weapons etc but just a rough guide of ballpark like 30 -50% of the 110kg weight allowance I am guessing. Am I way off? I am currently planning using hdpe 50mm in some areas and trying to shave weight off at the planning stage prior to purchase and build.

    Ta

  2. #2
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    Mainly build feathers but I run on a rule of thumb of 50% weight for chassis. I build in hardox mainly.

  3. #3
    TechAUmNu's Avatar
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    Euan Mutch
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    On our ring spinner the weapon is 34kg (31%) and the chassis is 43kg (39%)

  4. #4
    Eventorizon's Avatar
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    In an ideal world your Armour and Chassis are one and the same. Carbide, Apollo, Aftershock, Ironside 3, Eruption... all of them have a design where some, and in some cases all, of their armour forms the chassis. They use sheet Hardox to form a monocoque and then attach all the components inside on their own mounts. This doubling up on jobs for the same part of the robot frees up weight to be used elsewhere, or it means you can use the same amount of weight but its much stronger.

    This method is also a reasonably cheap and easy way of building a machine as you can cut the Hardox with an angle grinder and then weld it yourself if you have too. Most teams lasercut the parts to save the effort, but they tend to be the ones welding it up.

    Of course this isn't always possible, depending on your design, but even those that don't follow this method entirely find a place for it, usually in armour pods or single piece folded chassis.
    Last edited by Eventorizon; 11th September 2017 at 19:20.

  5. #5
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    Yes I agree the ideal is a monocoque chassis like most modern competitive robots just for difference and shock absorbance I would like to use hdpe but don't think it is hard enough by itself as a monocoque and only way is with it bolted to a metal space frame underneath in a heavyweight.

    Nylon as a supporting internal bulkheads but I dunno just throwing it out there! I've never worked with it before.

  6. #6
    maddox10's Avatar
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    Team RCC tried HDPE (semi)monocoque 30mm thick on Obsidian. It lasted 1 event.
    The HDPE welds are more brittle than the sheets, and bends tend to concentrate stress.

    For bulkheads, HDPE is good enough, except for applications where stiffness is needed, like in drives and weaponsupports. For that aluminium, glassfiber filled nylon or simular materials are better.

    For "historical and personal" references.
    Tough as Nails, the first machine to use Hardox , still is using the original monocoque jaws.
    Dented and battered. Sliced here and there in the last wars by 15 year younger spinners, still carrying the mark of the Beta Prototype, and not being smashed flat at the Peterborough Event end 2001 as everybody believed at that time .

    Bullfrog in the last version of Team RCC , events all over the UK, Mainland Europe and even Russia, the much changed flipperarm and pivot still were integrated in the hardox monocoque. Not the other way around.

  7. #7
    emisnug's Avatar
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    Big Dave 3's weight allocations are as follows:

    Chassis: 35KG
    Weapon (all rotating mass & bearings): 40KG
    Armour: 25KG
    Electronics etc: 10KG

    Although, with that being said, not quire sure how to differentiate between chassis and armour.

  8. #8
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    Chassis armour would be both the same in monocoque. If old school frame and armour welded/bolted onto the frame chassis would be frame and armour..well armour.

    With HDPE armour I suspect I will need to build frame and bolt on HDPE using insert nuts.

    I am aware this is inefficient weight wise but I believe this would be fairly resilient armour and easy to work.

    Would be resilient to impact from spinners but possibly vulnerable to tearing off the chassis if caught at an unlucky angle so will be testing various geometry of body shape.

    Anyways thank you for all the replies. Very helpful!
    Last edited by T00TY_FRU1TY; 12th September 2017 at 08:29.

  9. #9
    emisnug's Avatar
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    If you've not seen it, Ellis's excellent build diary on his latest featherweight, Neon, is well worth a read: https://www.facebook.com/teamrangleb...35472470090422

  10. #10
    maddox10's Avatar
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    The HPDE over a very resilient open frame isn't a bad idea , and there are some fine examples of that.
    Unfortunatly, never seen one done in any degree of succes in heavyweight.

    But don't worry about tear off. HDPE is sliced so easely that the opponent needs to hit a bolt to transfer a lot of force.

    Of course, that's taking in account how many bolts of what size and what surface of washer you're suing to keep the HDPE to the frame. Holding 0.25m² 30mm HDPE with 4 M5 bolts won't cut the cheese.

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